Yulun Zhang

High concentrations of particulate matter with diameters less than 2.5 μm (PM2.5) have seriously affected the sustainable economic and social development of Henan Province. Analysis of the temporal and spatial distribution of PM2.5 and source analysis can provide a scientific basis for local pollution prevention and control. Using data from 17 atmospheric monitoring stations from 2016 to 2018, the spatiotemporal evolution of PM2.5 concentrations and source apportionment of Henan Province was explored using spatial autocorrelation analysis, empirical orthogonal function (EOF), potential source contribution factor (PSCF) analysis, and concentration weight trajectory (CWT) analysis. The PM2.5 concentration demonstrated varied annual, seasonal, monthly and daily characteristics from 2016 to 2018. The annual average concentrations decreased each year at an average rate of 5.3 μg/m3. The seasonal variation was “low in spring and summer while high in autumn and winter”. The monthly average and daily average over-standard rates exhibited a U-shaped pattern, with low values in the summer and high values in the winter. The daily average presented a pulse-type fluctuation. The areas with high concentrations of PM2.5 were primarily distributed in the central and northern parts of Henan Province, while the areas with low values were primarily distributed in the southern part of Henan Province. PM2.5 concentrations were negatively correlated with temperature, with the highest concentration at 0-5ºC, and strongly positively correlated with relative humidity in winter, with the highest PM2.5 concentrations between 80% and 90% relative humidity. Overall, the most important pollution transmission in winter came from southern Shanxi and northern Shaanxi, followed by Anhui and Shandong, again from the Beijing-Tianjin-Hebei region, and the smallest transmission came from Hubei. The area within Henan Province was also a significant contributor.

The performance of the 20th century reanalysis (20CR) and of the pilot reanalysis of the 20th century (ERA‐20C) for Antarctic near‐surface air temperature is investigated based on quality‐controlled monthly temperature measurements with a time coverage of at least 15 years from 42 automatic and manual weather stations, and temperature reconstructions. On the inter‐annual timescale, ERA‐20C and 20CR agree well with the temperature observations since 1957/1958, but there are systematic biases relative to absolute values with cold bias at East Antarctic coastal stations, and warm bias over the inland stations. An abrupt upwards shift in Antarctic annual and seasonal (except summer) mean temperature averaged over the East Antarctic ice sheet and the Antarctic ice sheet occurs around 1950 in 20CR and around 1979 in ERA‐20C, which is probably related to the increasing counts of assimilated observations. Moreover, the significantly negative trends of seasonal and annual mean temperature in 20CR since the late 1970s are found to be largely spurious, which most likely results from the poor representation of variability in sea surface temperature (SST) around Antarctica in the 20CR's boundary forcing. These results imply and urge that caution must be taken when applying the two global reanalyses for evaluating long‐term climate changes at high southern latitudes.